1. Field of the Invention
The present invention relates to devices, systems and methods for remotely detecting concealed weapons, and particularly to system and methods for remotely detecting human carried explosives.
2. Description of the Related Art
The U.S. military and homeland security officials are keenly interested in new technologies that remotely detect Human Carried Explosives (HCE). The archetype threat is the suicide bomber. For example, on Mar. 2, 2004 three human suicide bombers detonated in a crowd in Baghdad, killing fifty-eight people and wounding more than two hundred. Other countries also have an interest in detecting terrorists carrying explosives on their person. Since September 2000, suicide bombers have killed over three hundred seventy-five Israeli civilians in over ninety separate attacks.
U.S. military commanders believe similar attacks will be carried out against military targets, and have placed a high priority on protecting forces from suicide bomber threats at home and abroad. Civilian law enforcement and corrections authorities are also highly interested in concealed weapons detection technologies. For example, the National Institute of Justice (NIJ) has funded the development of hidden weapon detection technology that works reasonably well when the subject is within fifteen meters of the detector. However, this range is well within the lethal zone of an HCE device, making such technologies ineffective for deployment for military force protection.
The ability to detect HCE devices concealed under clothing at distances up to one hundred meters would be extremely beneficial to military commanders concerned with protecting forces from human suicide bombers. By design, these weapons are impossible to detect visibly.
Many new technologies, including non-lethal suppression devices, are being developed to stop threats as they enter the mitigation zone. In addition, a great deal of effort is underway to improve existing technologies capable of identifying concealed threats at close-in ranges up to fifteen meters. These include infrared, ultrasound, X-ray, magnetometers, and imaging radars.
However, infrared sensing is impractical due to very small temperature contrasts between a hidden weapon and outer layers of clothing. Ultrasound is inexpensive and readily available; however, it is less effective at penetrating heavy clothing than radar. X-ray and magnetic portal detectors have proven much more effective at detecting both metallic and non-metallic concealed weapons, but portal detection technologies are inherently limited by the inability to operate such devices at a distance.
Currently, no technologies exist to reliably detect HCE devices at standoff (safe evacuation) ranges. According to Explosive Ordinance Disposal guidelines, the safe evacuation distance is proportional to the cube root of the device weight multiplied by a destruction factor that varies with munitions type. A typical suicide bomber payload consisting of thirty pounds of explosive surrounded by fragmentary shrapnel yields a safe evacuation distance of approximately one hundred meters. Similarly, a Claymore mine with a shaped charge has a safe evacuation distance of approximately one hundred meters, whereas a car bomb typically has a safe evacuation distance of four hundred fifty-seven meters.
Although radar easily reaches potential threats at safe evacuation distances (standoff ranges), devices lacking metal fragmentation are transparent to conventional radar solutions. Moreover, conventional radar solutions that rely on radar cross section (RCS) measurements alone cannot reliably discriminate between humans, humans with body clutter (e.g., cell phone, belt buckle, etc.), and humans carrying fragmentation and explosives.
In order to separate a potential detection from random materials in the background environment of a potential threat and to localize a detection to a specific individual, a sensor is required having a small enough field of view so that it has enough resolution on a single individual being interrogated as a potential threat that a positive detection can be associated with the individual separate from his background and other individuals around him. Solving this problem requires a sensor with a relatively narrow field of view (FOV) of approximately a one-half to one degree visual arc at 100 meters if the sensor's FOV is going to correspond to one individual person. Such a narrow FOV requires some precise method for pointing the sensor at potential threats.
To examine a useful field of regard (FOR), for example, 600 of visual arc, the sensor must be moved sequentially to every potential individual who might be carrying an explosive device. Returns from vehicles, buildings, signs, and other objects in the background must be ignored. Many proposed detection systems postulate a skilled human operator to point the device at individual potential threats to solve this problem. However, suicide bombers have been observed to have been driven near to their target by accomplices and then to have exited the vehicle and to have run to their target and detonate. Consequently, the time to detect and interdict a suicide bomber may be only tens of seconds, and a practical system will have a method to continuously scan and examine all potential threats in a field of regard. Examining and identifying individual people at distances greater than 25 meters and rapidly pointing a narrow FOV detection sensor at each in turn covering a wide FOR every few seconds is beyond the capability of human operators in situations with more than a few potential threats.
In addition to requiring the human operator to point the sensor precisely at numerous potential threats in rapid succession, previously proposed systems also require that a skilled human operator simultaneously examine the output of the sensor to make a subjective judgment as to the likelihood that a given person is a threat. It is unlikely that any proposed system will be effective if more than a few people could be in the field of regard at any one time. In order to meet these demanding timelines of precise pointing and analysis of the sensor's output, a system that provides a method to cue a narrow field of view sensor in a rapid, precise, and automated fashion and that has a method for automatically accessing the likelihood of a threat based on processing of the narrow FOV sensors signals is required.
Bomb detection technologies generally fall into two categories: direct methods designed to detect high explosives based on chemical properties, and indirect methods that look for anomalous signatures associated with bomb devices. None of these techniques are capable of detecting HCE threats at standoff ranges.
Direct methods for bomb detection exploit the fact that high explosives contain large amounts of nitrogen and oxygen in their molecular composition. Both bulk and trace detection methods use sampling methods designed to measure the chemical properties of the material, and both require that the material be placed in close proximity to the sensor. The main application of direct explosive detection methods is in portal systems.
Bulk detection methods measure the interaction between the sample under investigation and a penetrating radiation wave, such as ionizing radiation or electromagnetic radiation. Bulk detection methods can be used on sealed packages, including concealed threats. However, methods that use ionizing radiation may not be suitable for use in screening of human subjects.
Trace detection methods are based on direct interaction with the material and require that some amount of the explosive be present on the outside of the package in the form of particle residue or vapors. Both canines and gas chromatography methods ingest vapors and hence need to be close enough to the suspect article to acquire a sample of the vapor. Particle-based detection methods, such as laser ionizing mass spectroscopy, use optical methods for interrogating samples, but detector noise limitations require that the sample be proximal to the laser.
Indirect detection methods are designed to detect anomalies in human signatures that are consistent with concealed bomb devices. As with direct detection methods, the current standard practice is limited to short-range or portal based systems. Metal detectors are used to detect the presence of metal fragmentation and are of questionable use against devices that do not employ metallic fragmentation. Thermal and passive millimeter wave (MMW) systems exploit the fact that human skin reflectivity differs from that of metal or explosive materials. Both thermal and MMW radiation pass through clothing. Passive imaging systems collect an image of devices concealed under clothing in outdoor settings using the illumination of the cold sky. Imaging devices require trained operators to point the device and interpret the images, resulting in an increase in labor and privacy concerns, and in longer times to check each potential threat.
Various devices have been developed applying the above principles. U.S. Pat. No. 4,975,968, issued to T. Uki in December 1990, discloses a dielectrometry monitoring method and apparatus for three-dimensional profiling and colorable imaging of the material contents of articles carried on a conveyor belt. U.S. Pat. Nos. 5,073,782 and 5,227,800, issued to Huguenin et al. in December 1991 and July 1993, respectively, disclose a contraband detection system suitable for detecting concealed non-metallic contraband, such as ceramic or plastic weapons or illegal drugs using quasi-coherent millimeter wave radiation. The Huguenin system is an active imaging system designed for detecting contraband on a conveyor belt with a constant background at close range. Polarized returns are used by an operator to adjust contrast with the background, and a skilled operator is required to interpret the images as the conveyor scrolls objects past the sensor.
U.S. Pat. No. 5,177,445, issued to T. Cross in January 1993, discloses a method by which particular non-metallic materials are detected by recognizing the way in which their electrical properties vary with the frequency of an applied alternating electric field. U.S. Pat. No. 5,592,170, issued to Price et al. in January 1997, discloses a frequency-agile, narrow-instantaneous bandwidth radar system which detects objects and discriminates between different types of objects from a safe stand-off distance. The field of regard, however, is fixed and is dependent upon manual sweeping of an area under surveillance by a skilled human operator. A skilled operator would have difficulty in accurately pointing and tracking a person with a 1° radar beam at ranges greater than short standoff distances. In the Price system, the discrimination of threats is also performed manually by a skilled human operator.
Unlike the previous devices that detect concealed weapons, U.S. Pat. No. 5,829,437, issued to J. Bridges in November 1998, discloses a system and method by which cancers in heterogeneous tissue is located and detected by using the backscatter signal returns from microwave radiation. Unlike the previously disclosed devices, the '437 device is not a stand-off device and requires contact with the patient.
U.S. Pat. Nos. 6,243,036 and 6,342,696, issued to G. Chadwick in June 2001 and January 2003, respectively, disclose methods and apparatuses for detecting objects by comparing the differences in amplitudes of polarized radiation reflecting off a target illuminated with low-power polarized radiation with a predetermined value representative of an expected difference if the object were not present. The Chadwick patents are specifically illustrated by examples devoted to the detection of handguns, generally from laboratory studies, and do not address the problem of focusing the radar over a wide field at ranges up to one hundred meters or greater, and do not address the problem of detecting and identifying human subjects at such ranges, nor the problem of detecting nonmetallic objects by radar.
U.S. Pat. No. 6,359,582, issued to MacAleese et al. in March 2002, discloses a weapons detector utilizing a handheld radar system and signal processor to detect the presence of a plurality of self-resonant frequencies in the backscattered signals of a target between 4–15 yards. Although suitable for guns and similar devices, HCE devices must be detected at a much greater stand-off distance.
The aforementioned devices have a fixed field of regard and require an operator to direct the field of regard of the sensor upon the subject matter. U.S. Pat. No. 6,507,366, issued to H. Lee in January 2003, on the other hand, is a device that automatically tracks a moving object using a camera having a zoom lens, an auto focus lens and a charge-coupled device for converting an image into electrical signals. The disclosure, however, is silent on how the device manipulates multiple moving targets.
Articles entitled “Radar-Based Intruder Detection for a Robotic Security System”, Cory, et al., SPIE Proc. 3525:Mobile Robots XIII and Intelligent Transportation Systems, Boston, Mass., 1–5 November 1998, pp. 62–72, “Mobile Robots for Outdoor Security Applications”, Pastore et al., American Nuclear Society 8th International Topical Meeting on Robotics and Remote Systems (ANS'99), Pittsburgh, Pa., 25–29 April 1999, and “Robotic Security Systems”, Everett, H. R., IEEE Instrumentation and Measurement Magazine, December 2003, pp. 30–34 describe a robotic system for the detection of intruders in storage yards, arsenals, and the like. The system includes an infrared/vision based system (FLIR) and a millimeter wave radar at 77 GHz slaved to the vision system on a two-axis pan and tilt mechanism. The vision system is stepped across a field of interest, and when motion is detected, a target track is established. The vision system is used to define geometric shape and angular location, and Doppler radar pulses provide range and speed of movement, which are fused to establish a radar cross section and to confirm target and range. The system has been reported successful in detecting a human at ranges of 100 m–300 m. A scanning radar is added to the system for 360° detection of other potential targets while the system is tracking an initial target.
None of the above inventions and patents, taken either singly or in combination, is seen to describe the instant invention as claimed. Thus, the system and method for standoff detection of human carried explosives of the present invention solving the aforementioned problems is desired.